Update docs to include placeholder image functionality

docs/docs/v3/README.md

@@ -50,7 +50,7 @@ listed in <Link name="commonmark-spec" /> are supported (including support for *
   * Blockquote (`blockquote`)
   * Heading (`h1`, `h2`, `h3`, `h4`, `h5`, `h6`)
   * there is support to render any HTML tag, but it will require to create a special `TagHandler`,
-    more information can be found in [HTML section](/docs/v3/html/custom-tag-handler.md)
+    more information can be found in [HTML section](/docs/v3/core/html-renderer.md)
 * [Task lists](/docs/v3/ext-tasklist/):
 - [ ] Not _done_
   - [X] **Done** with `X`

docs/docs/v3/core/images.md

@@ -145,8 +145,6 @@ If you want to display GIF or SVG images also, you can use [image-gif](/docs/v3/
 and [image-svg](/docs/v3/image/svg.md) modules.
 :::
 
-## 
-
 :::tip
 If you are using [html](/docs/v3/html/) you do not have to additionally setup
 images displayed via `<img>` tag, as `HtmlPlugin` automatically uses configured
@@ -157,3 +155,51 @@ sizes, which is not supported natively by markdown, allowing absolute or relativ
 <img src="./assets/my-image" width="100%">
 ```
 :::
+
+## Placeholder drawable <Badge text="3.0.0" />
+
+It's possible to provide a custom placeholder for an image (whilst it's loading).
+
+```java
+final Markwon markwon = Markwon.builder(context)
+        .usePlugin(ImagesPlugin.create(context))
+        .usePlugin(new AbstractMarkwonPlugin() {
+            @Override
+            public void configureImages(@NonNull AsyncDrawableLoader.Builder builder) {
+                builder.placeholderDrawableProvider(new AsyncDrawableLoader.DrawableProvider() {
+                    @Override
+                    public Drawable provide() {
+                        // your custom placeholder drawable
+                        return new PlaceholderDrawable();
+                    }
+                });
+            }
+        });
+```
+
+## Error drawable <Badge text="3.0.0" />
+
+To fallback in case of error whilst loading an image, an `error drawable` can be used:
+
+
+```java
+final Markwon markwon = Markwon.builder(context)
+        .usePlugin(ImagesPlugin.create(context))
+        .usePlugin(new AbstractMarkwonPlugin() {
+            @Override
+            public void configureImages(@NonNull AsyncDrawableLoader.Builder builder) {
+                builder.errorDrawableProvider(new AsyncDrawableLoader.DrawableProvider() {
+                    @Override
+                    public Drawable provide() {
+                        // your custom error drawable
+                        return new MyErrorDrawable();
+                    }
+                });
+            }
+        });
+```
+
+:::warning
+Before `3.0.0` `AsyncDrawableLoader` accepted a simple `Drawable` as error drawable
+argument. Starting `3.0.0` it accepts a `DrawableProvider` instead.
+:::

docs/docs/v3/migration-2-3.md

@@ -8,3 +8,5 @@
 * HTML no longer _implicitly_ added to core functionality, it must be specified __explicitly__ (as an artifact)
 * removed `markwon-view` module
 * changed Maven artifacts group to `ru.noties.markwon`
+* removed `errorDrawable` in AsyncDrawableLoader in favor of a drawable provider
+* added placeholder for AsyncDrawableProvider